Letter to the Editor

The evolution of the gas fraction of quiescent galaxies modeled as a consequence of their creation rate

¹ Instituto de Física, Pontificia Universidad Católica de Valparaíso, Casilla 4059, Valparaíso, Chile
e-mail: raphael.gobat@pucv.cl
² Cosmic Dawn Center (DAWN), Copenhagen, Denmark
³ DTU-Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
⁴ University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
⁵ CEA, Irfu, DAp, AIM, Université Paris-Saclay, Université de Paris, CNRS, 91191 Gif-sur-Yvette, France

Received: 5 October 2020
Accepted: 16 November 2020

Abstract

We discuss the evolution of the interstellar medium of quiescent galaxies, currently emerging from recent analyses, with the help of a simple model based on well-established empirical relations such as the stellar mass functions and the main sequence of star formation. This model is meant to describe observed quantities without making specific assumptions on the nature of quenching processes, but relying on their observable consequences. We find that the high gas fractions seen or suggested at high redshift in quiescent galaxies, and their apparent mild evolution at early times, can be mostly attributed to a progenitor effect where recently quenched galaxies with ∼10% gas fractions dominate the quiescent galaxy population until z ∼ 1. In the same context, the much lower gas and dust fractions measured in local early-type galaxies are interpreted as the product of the steady depletion of their interstellar medium on a ∼2 Gyr timescale, coupled with a higher fraction of more gas-exhaustive events.